Vacuum-tube circuits



March 18, 1930. R. 1.. DAVIS El AL 1, ,2

VACUUM TUBE CIRCUITS Filed April 15 1925 INVE 5 Donald G. e and Robert L. Dav/s.

, 'A'TTORN-EY Patented Mar. 18, 1930 UNITED STATES PATENT OFFICE ROBERT L. DAVIS AND DONALD G. LITTLE, OF WILKINSIBURG, PENNSYLVANIA, AS

SIGNORS TO WESTINGHOUSE P ORATION OF PENNSYLVANIA ELECTRIC & MANUFACTURING COMPANY, A. COR- VACUUM-TUBE cmcurrs Application filed April 15, 1925. Serial No. 23,429.

This invention relates to vacuum tube devices and particularly to vacuum tube generators of very high frequencies.

It is an obiect of this invention to distribute the heating effect of the space current over a greater extent of the filament, whereby the life of the tube is increased.

It has been found that with very short waves, the results obtained are better if provision is made for the space current to pass out of the tube over both ends of the filament,

instead of over one end only.

It is usual in oscillation generators to provide an oscillating circuit, one point of which is at a potential but slightly different from that of the ground. Owing to difficulties in exact balancing, it is not possible to have the potential of said point exactly that of the ground. A metallic connection, from the point intended to be at ground potential, to the ground will, therefore, carry some high frequency current. It is a further object of this invention to provide for conveying this high frequency current, over two paths, from the ground to the two ends of the filament.

Other objects of the invention will be ap-. parent from the following detailed descrip-' cluding the direct-current source. comprisesa choke oil 6, and is connected to the oscillating circuit 7 through a reactor 8. This reactor is illustrated as a condenser but an inductor may also be used.

The oscillating circuit 7 comprise.- a com denser 9, which may be the capacity of an antenna if desired, and an inductor 11 in parallel with the condenser 9.

A tap 12 is adjustably connected to the inductor 11. Preferably this connection is at the electrical center of the inductor, whereby the potential of the tap 12 is only slightly different from that of the ground 13. It is 8, affords a connection for the grid 15 of the tube 1. This connection includes a grid-biasing device. Any form of grid-biasing device, such as a battery, may be used. I have chosen for illustration a condenser 16 in parallel with a high resistance 17 The filament 2 has two conductors extending to the outside of the tube 1, one of said conductors for each end of the filament. A condenser 18 is connected to one of said conductors and tothe ground. As illustrated, a connection to the ground is by way of the conductor 12, which is united to the conductor extending to the other end of the filament. It is, however, obvious that the condenser 18 may be provided with a distinct ground if desired. The condenser 18 acts as a stopping condenser, preventing the short circuit of the source 3 of heating current.

In the operation of the device, oscillations are set up in thecircuit 7 and maintained by energy supplied from the source 5. The tube 1 generates these oscillations in a way that is'familiar to those skilled in the art and need not be recited here. As a consequence of this action, a high-frequency component is present in the space current between the plate '4 and the filament 2. This high-frequency invention causes the radio-frequency space current to divide, passing out of the tube by both ends of the filament. Its heating efiect is, therefore, distributed over a greater portion of the filament and the life of the filament will be longer on this account.

The impedance ofiered by the condenser 18 to the high-frequency space current is small. For a high-power set working at a wavelength-of about .90 meters, I have found .25 microfarad enough for this condenser, although it can, without disadvantage, be .as

- large as two microfarads. The condenser can readily be so designed that the space current divides practically equally between the two exits from the tube. Even when this is not done, the advantages of this invention can be secured by making the condenser of such size that a substantial portion of the space current passes throughout the condenser.

Many variations inthe application of this invention and in the details ofconstruction will readily occur to those skilled in the art. The specific illustration and description of only a single form' is not intended as a limitation. N0 limitation except that required by the prior art or explicitly stated in the claims is intended.

I, claim as my invention:

1. In an oscillator, a vacuum tube having three electrodes, namely, a plate, a filament and a grid, a source of heating current for said filament, an oscillationcircuit, a source of energy, means so relating said oscillation circuit, said electrodes and said source that oscillations are maintained in said oscillation circuit, said means including a conductor uniting one end of said filament to a point of small potential in said oscillating circuit,

said conductor being grounded, and means including a condenser for grounding the other end of said filament.

2. In a vacuum-tube radio-frequency generator, a cathode having two terminals external to the tube, a radio-frequency tuned circuit, a connection from the anode to the source of power, a connection of smaller impedance to radio frequency than to low frequency extending betweensaid terminals and a common connection distinct froms aid interterminal connection maintaining one of said terminals, a point of said tuned circuit and one pole ofsaid source at ground potential.

3. In combination, a power-tube device adapted to generate oscillations at radio-frequencies, said tube-device comprising a cathode having external terminals, a large condenser permanently connected between said terminals, and means distinct from said condenser for maintaining one of said terminals at ground-potential In testimony whereof, we have hereunto subscribed our names this 6th day of April,

. ROBERT L. DAVIS.

DONALD G. LITTLE. 

